(1) Field of the Invention
The present invention relates to an image forming apparatus and particularly to an image forming apparatus having a paper type identification device.
(2) Description of the Related Art
Traditionally, the number of types of media has increased on which color images are to be printed in an image forming apparatus or the like such as a multifunction color copier (multifunction peripheral or MFP). Even when papers alone are considered as print media, various types of papers that are different in thickness or the like are used.
Such paper types are usually distinguished by grammage (g/m2), which shows the weight per predetermined area. For example, papers within ranges of 64-105, 106-163, 164-209, 210-256, and 257-300 are respectively called plain paper, thick paper 1, thick paper 2, thick paper 3, and thick paper 4. The grammage depends on the density and thickness of paper, but if the density of paper is constant, they will be proportionate to the thickness.
If the paper type, that is, the thickness and density of paper differs in this manner, optimum printing conditions to acquire a satisfactory print image differ. Generally, as the thickness of paper increases, the fixing temperature of an image that has been made visible falls quickly. If the image is fixed at the same temperature, a fixation defect, or wait and stop due to the lowering of the temperature occurs, and a satisfactory print image cannot be acquired. Thus, to acquire a satisfactory print image, it is necessary to distinguish a paper for printing.
Traditionally, such identification of a paper type is carried out as a user inputs the thickness and grammage on a screen displayed on a control panel of the multifunction peripheral. In accordance with the inputted thickness and grammage of the paper, fixation of a visible image, the speed of carrying the paper and the like are controlled.
However, except for the case where recording papers are set in a recording paper housing cassette, the user rarely knows the thickness of the papers or the like very well. Therefore, the paper type is erroneously set, a satisfactory print image cannot be acquired, and recording papers are often wasted.
Thus, an image multifunction peripheral is known in which the thickness or the like of papers housed in a recording paper housing cassette is automatically detected and in which, for a thick recording paper, a separately provided fixing auxiliary power source is driven to perform satisfactory printing (see JP-A-11-24512).
However, in the apparatus in which the thickness of paper is detected by a medium sensor, the thickness of a recording paper is detected when the recording paper is pulled out from the recording paper housing cassette as described above. Therefore, there is a problem that a sufficient time cannot be taken before an image is actually printed and therefore a satisfactory print image cannot be acquired, or that if a sufficient time is taken before printing, the overall printing time becomes longer.
A light emission quantity adjustment apparatus is also known in which the thickness of a medium is detected and the quantity of light emission of a light-transmitting sensor arranged within the apparatus is adjusted (JP-A-9-113230).